In crown and bridge prosthodontics, metal copings are conventionally used to provide the essential structural strength and rigidity necessary for a dental restoration to resist the forces of mastication. In a ceramic-to-metal dental restoration, the metal coping forms the understructure, over which is applied a fired-on coating of porcelain or an acrylic veneer.
The metal coping may be cast from an investment of a wax or plastic pattern of the tooth to be restored. An alternative procedure which does not require waxing, investing or casting and which currently has been gaining wide acceptance by many laboratory practitioners and dentists is to form the coping from a moldable dental material composition composed of a mixture of high and low fusing temperature metal particles, as disclosed, for example, in U.S. Pat. No. 5,593,305 and U.S. Pat. No. 5,914,185 respectively. The dental material as taught in these patents, the disclosure of which is herein incorporated by reference, forms a porous structure upon heat treatment having a high void volume of above at least 20%. Before heat treatment the dental material is molded into the shape of the tooth to be restored. The molded shape is self-supported and is converted upon heat treatment in a dental furnace into a porous structure essentially any without shrinkage.
In the completion of a dental restoration the metal coping is cemented to the tooth preparation. However, if the metal coping is not properly cemented or if the cement does not retain itself between the surface of the prepared tooth and the metal dental coping microleakage may occur which will lead to decay and infection. In fact, microleakage is a major factor in promoting tooth decay under a dental restoration and particularly at the cervical margin. Accordingly, retention of the cement between the surface of the prepared tooth and the metal dental coping is an important factor in the preparation of dental crown or bridge.